The invention herein resides in the art of apparatus and techniques for cutting and forming tread designs in rubber-based tires. Particularly, the invention relates to such apparatus and technique for grooving or otherwise removing rubber from large off-the-road tires, thereby forming a lug or tread design. The invention automatically regulates, under programmed control, relative motions in five axes to achieve the desired grooving for the tire tread while further including means for regulating and maintaining preselected temperatures on the cutting knife during the grooving operation.
The prior art has slowly progressed in the field of tire tread forming to the point where plural axes may be controlled by a programmed cutting apparatus. Indeed, applicants find the state of the art to be best exemplified in U.S. Pat. Nos. 3,075,575; 3,589,427; 4,080,230; and 4,081,017. An analysis of the state of the art from such references illustrates an absence of sufficient control over the parameters of concern in grooving a tire to achieve cost effective and reliable grooving operations.
The prior art is devoid of any tire grooving machine which is capable of simultaneously controlling movement about five axes by means of automatic adjustment and interpolation of composite movement in each of the axes. Further, the prior art is devoid of any tire grooving apparatus wherein a turret control of the blade is maintained to affectuate cuts in the sidewall of the tire. There is no provision for the regulation of knife current to maintain a preselected temperature or to vary that temperature in accordance with the contour or depth of cut. Indeed, in the prior art, it has been virtually impossible to cut treads into tires which have been cured since the prior art did not have sufficient knife strength or current regulation to achieve such a cut. While green rubber, being of a soft pliable nature, is easy to cut, high temperatures of accurate regulation are necessary for cutting cured rubber. Further shortcomings of the prior art include limited axial rotation of the cutting knife with an inability to effect circumferential cuts. The prior art has also taught that the tire be cut in a deflated posture and, while such may result in satisfactory cutting of green rubber, a deflated tire has insufficient rigidity to withstand the forces imparted in cutting cured rubber. Yet further, the prior art has been devoid of a means for automatically programming an apparatus for cutting a desired tread design by merely tracing such design on a used or rejected tire carcass.